The present invention relates to a cooler arrangement for a combustion engine and particulary to separaying cooled exhaust gases and gases cooled in a charge air cooler.
The amount of air which can be supplied to a supercharged combustion engine depends on the pressure of the air but also on the temperature of the air. Supplying the largest possible amount of air to the combustion engine therefore entails cooling the compressed air in a charge air cooler before it is led to the combustion engine. The compressed air is usually cooled by ambient air flowing through the charge air cooler. The compressed air can thus be cooled to a temperature substantially corresponding to the temperature of the surroundings.
The technique known as EGR (Exhaust Gas Recirculation) is a known way of leading part of the exhaust gases from a combustion process in a combustion engine back, via a return line, to an inlet line for supply of air to the combustion engine. A mixture of air and exhaust gases is thus supplied via the inlet line to the engine's cylinders in which the combustion takes place. The addition of exhaust gases to the air causes a lower combustion temperature resulting inter alia in a reduced content of nitrogen oxides NOx in the exhaust gases. This technique is used for both Otto engines and diesel engines. A known practice is to cool the returned exhaust gases in a first EGR cooler by means of the coolant of the vehicle's cooling system and in a second EGR cooler by means of ambient air. The exhaust gases can thus likewise be cooled to a temperature substantially corresponding to the temperature of the surroundings. A further known practice is to arrange the charge air cooler and the second EGR cooler close to one another at a front portion of a vehicle in front of the vehicle's ordinary radiator. The cooled exhaust gases and the cooled compressed air can thus be mixed with one another substantially immediately after the cooling.
In operating situations where the combustion engine's load is low while at the same time there is a low ambient temperature, there is risk of the exhaust gases being cooled to such a low temperature that corrosive substances in the exhaust gases may condense during cooling in the EGR cooler. EGR coolers are usually made of corrosion-resistant material such as stainless steel so that no problems are caused, at least during short periods, by the formation of such condensate in the EGR cooler. Charge air coolers, however, are usually made of material such as aluminium which has good heat-conducting characteristics but less good corrosion-resistant characteristics. As the charge air cooler and the EGR cooler are in this case situated close to one another, there is risk of exhaust gases or condensate from the exhaust gases making their way into and accumulating in the charge air cooler, which is not made of a totally corrosive-resistant material.